Every buffer has one major mode that provides its main editing or application behavior. A source buffer uses a programming-language mode, Dired uses a mode for directories, EWW uses one for Web pages, and Org uses one for structured notes and documents. Minor modes add optional behavior alongside the major mode.
This context is what makes Emacs efficient: a movement command can move by a sentence in prose, a heading in an outline, an item in a list, or another meaningful unit supplied by the active mode. Emacsvox speaks the result of the operation and can use the same context to announce state changes.
You do not need to predict which commands every mode provides. Press C-h m in the buffer you are using, then C-h k followed by a key when you want a fuller explanation. See Find Help While You Work provides a short practical guide to these discovery commands.